1. Field of the Invention
The present invention generally relates to digital cameras and more particularly relates to digital color cameras that use four sensors, three for the tricolor sensing and the fourth for full-color sensing to improve the qualities of digital images therefrom.
2. Description of the Related Art
Digital photography is one of the most exciting technologies to emerge during the twentieth century. With the appropriate hardware and software (and a little knowledge), anyone can put the principles of digital photography to work. Digital cameras are on the cutting edge of digital photography. Recent product introductions, technological advancements, and price cuts, along with the emergence of email and the World Wide Web, have helped make digital cameras the hottest new category of consumer electronics products.
Digital cameras, however, do not work in the way as the traditional film cameras do. In fact, they are more closely related to computer scanners, copiers, or fax machines. Most digital cameras use an image sensor or photosensitive device, such as charged-coupled device (CCD) or Complementary Metal-Oxide Semiconductor (CMOS) to sense a scene. The photosensitive device reacts to light reflected from the scene and can translate the strength of that reaction into a numeric equivalent. By passing light through red, green, and blue filters, for example, the reaction can be gauged for each separate color spectrum. When the readings are combined and evaluated via software, the camera can determine the specific color of each segment of the picture. Because the image is actually a collection of numeric data, it can easily be downloaded into a computer and manipulated for more artistic effects.
Nevertheless, there are many cases in which digital cameras simply could not be used due to the limited resolutions from today""s digital cameras. Film-based photographs have immeasurably higher resolutions than digital cameras. The comparison magnitude may be somewhere millions of pixels versus tens thousands of pixels in the digital cameras. Although, it is theoretically possible to design a photosensitive chip with multimillion of pixels, the cost of such chip would be a forbidden number and may consequently drag the digital cameras out of the consumer market.
FIG. 1 shows a typical image sensor or photosensitive chip 100 used in digital cameras. Photosensitive chip 100 comprises a plurality of photocells arranged in an array. A mosaic of selectively transmissive filters is superimposed in registration with each of the photocells so that a first, second and third selective group of photocells are made to sense the red, green and blue range of the visible spectrum, respectively. The number of the photocells in photosensitive chip 100 typically determines the resolutions of digital images resulting therefrom. The horizontal resolution is by the number of the photocells in a row 102 and the vertical resolution is by the number of the photocells in a column 104. Because of the alternating positions of the designated photocells, for example, 106 for red photocells and 108 for green photocells, the actual resolutions for a color image have been significantly reduced.
To have color images with higher resolutions, the number of photocells in a sensor must be increased. The actual design and manufacturing cost for a higher resolution sensor, however, would be evaluated at many magnitudes of the lower resolution sensors. Therefore there is a great need for a generic solution that makes digital cameras capable of producing high resolution images without enormously incurring the cost of photosensitive chips with multimillion photocells.
A second noticeable quality between digital cameras and film-based cameras is the dynamic range. Films have the necessary chemical pigments to make colors much more vivid and more adaptive to light conditions than current digital cameras can do. This is largely due to the limited pixel depth the current digital cameras could produce and the limited sensitivity of the photocells in the image sensor. There is thus a further need for digital cameras that produce better colors and details in a greater range.
There are many other quality factors that limit the popularity of digital cameras although it is well understood that the digital cameras are the much preferred image acquisition means. Solutions that fundamentally improve the image qualities without incurring substantial cost are always welcome and being seriously and continuously sought.
Recent product introductions, technological advancements, and price cuts, along with the emergence of email and the World Wide Web, have helped make digital cameras the hottest new category of consumer electronics products. But the image qualities, noticeably the image resolutions and color dynamic ranges, have limited the popularity of digital cameras among consumers. Under the constraints of improving image qualities without incurring substantial costs to the digital cameras, the present invention discloses improved digital cameras that use multiple image sensors with multiple lenses.
The present invention has been made in consideration of the above described problems and needs and has particular applications to digital cameras that are demanded to produce digital images of high qualities. According to one aspect of the present invention, an improved digital camera uses four image sensors, each having its own lens, of which three image sensors are made responsive to the three primary colors and the fourth one made responsive to all intensity information. Using a set of digital image processes embedded in a digital signal processing chip, images from the three color image sensors are processed with reference to the image from the black-and-white image sensor and subsequently produce high quality and film-like true color digital images.
With the unique configuration, there are many obvious benefits and advantages. First, the resolutions of the image sensors are fully used. Second each of the image sensors is only responsible for one color; thereby the expensive process of coating a mosaic of selectively transmissive filters superimposed in pixel-based registration on one image sensor is eliminated and subsequently no micro-lenses process is needed. Third, the image from the black-and-white image sensor captures all information including details that the three color image sensors may have missed. Further, because the resolutions of the image sensors are fully used, for the same resolution of color images, the image sensors would relatively have smaller number of pixels, which typically leads to high yield, higher sensitivity, less cross-talking, and lower clocking rate. Besides, the size of the image sensors could be smaller, resulting in smaller optical lenses.
According to one embodiment, the present invention is an improved digital camera comprising:
four image sensors, closely positioned with respect to a common plane,
four lenses, each mounted in front of one of the four image sensors;
first three of the four image sensors being respectively sensitive to three different regions of visible color spectrum; a fourth sensor of the four image sensors being sensitive to a full region of the visible color spectrum; the full region including the three different regions in the visible color spectrum;
the four image sensors producing, independently and respectively, four intensity images when being exposed to an imaging target, first three images of the four intensity images respectively from the first three of the four image sensors and a fourth image of the four intensity images from the fourth sensor of the four image sensors;
an analog-to-digital converting circuitry coupled to the four image sensors and digitizing the four intensity images to produce four digital images; first three of the four digital images corresponding to the first three images and a fourth digital image of the four digital images corresponding to the fourth image of the four intensity images;
an image memory, coupled to the analog-to-digital converting circuitry, for storing the four digital images; and
a digital image processing circuitry coupled to the image memory and receiving the four digital images, producing a color image of the imaging target from the four digital images.
According to one embodiment, the present invention is a method for producing digital images of high qualities, the method comprising:
obtaining three scalar images from three image sensors closely positioned in a common plane with reference to an image target;
obtaining a gray intensity image from a fourth image sensor, the fourth image sensor closely positioned in the common plane with the three image sensors;
digitizing the three scalar intensity images and the gray intensity image to produce three scalar digital images and a gray digital image;
buffering the three scalar digital images and the gray digital image in an image memory; and
producing a color image from the three scalar digital images processed in conjunction with the gray digital image.